1. Technical Field
This disclosure relates generally to a perforated flow body surface through which suction may occur in order to maintain laminar flow of a fluid on the surface of the body, and methods for forming such perforated surfaces.
2. Background Information
Achieving laminar flow over aircraft aerodynamic surfaces has been a goal for many decades because, in general, laminar flow over an aerodynamic surface results in reduced drag compared to turbulent flow over the same surface. Two strategies include natural laminar flow and active laminar flow control.
Natural laminar flow (NLF) is produced by shaping the aerodynamic surfaces in a manner such that laminar flow naturally occurs and is maintained along the extent of the aerodynamic surface during all or during targeted flight conditions. NLF is desirable because it does not require any additional hardware or controls. However, it is not practical to shape certain aerodynamic surfaces to achieve NLF.
Active laminar flow control (ALFC) involves modifying the air flow over an aerodynamic surface so that laminar flow, which occurs over the leading edge, is maintained over the extent of the surface by preventing a trip to turbulent flow. The modification to the air flow for ALFC can take different forms, one of which involves continuously removing low energy air from boundary layer along the extent of the flow surface to prevent the boundary from thickening and eventually tripping to turbulent flow. This has been proposed through using many small holes closely spaced and generally evenly distributed along and across the flow surface with suction to pull air from the boundary layer into the holes in a generally continuous fashion.
While ALFC through suction removal of the boundary layer has been proposed for many decades, it has not been commercially implemented due to several problems. One problem is the cost of forming the many very small, closely spaced and distributed holes on the air flow surface. This disclosure addresses, among other things, the problem of how to economically form these holes in a repeatable, controllable manufacturing process in the types of materials and in the structures commonly used for aircraft aerodynamic surfaces.